MaxScale, RDS and the ReadWriteSplit Router

[Wagner Bianchi]

Hello Folks,

I see a different scenario with MaxScale 2.5.11, when I have the MariaDBMon Monitor, the ReadWriteSplit Router and a master and slave, both running the MySQL 5.7.33 on AWS RDS. 

The case is that I only see connections open to the master while I also see the number of connections for the replica always like 0.

root@maxscale01: ~ # maxctrl list servers --tsv

dbmaster teste-maxscale.[...].com 3306 13 Master, Running

dbreplica teste-maxscale-read.[...].com 3306 0 Slave of External Server, Running

My configuration is below:

[cluster-monitor]

type=monitor

module=mariadbmon

user=maxmon

password=B13...

servers=dbmaster,dbreplica

monitor_interval=500

backend_connect_timeout=3s

backend_read_timeout=3s

backend_write_timeout=3s

backend_connect_attempts=1

journal_max_age=28800s

disk_space_check_interval=0ms

script_timeout=90s

events=all

failcount=5

ignore_external_masters=false

auto_failover=false

failover_timeout=90s

switchover_timeout=90s

replication_master_ssl=false

verify_master_failure=true

master_failure_timeout=10s

auto_rejoin=false

enforce_read_only_slaves=false

switchover_on_low_disk_space=false

maintenance_on_low_disk_space=true

handle_events=true

assume_unique_hostnames=true

enforce_simple_topology=false

cooperative_monitoring_locks=none

master_conditions=primary_monitor_master

slave_conditions=none

[dbmaster]

address=teste-maxscale.[...].com

extra_port=0

persistmaxtime=0ms

persistpoolmax=0

port=3306

priority=0

protocol=mariadbbackend

proxy_protocol=false

rank=primary

ssl=false

ssl_cert_verify_depth=9

ssl_verify_peer_certificate=false

ssl_verify_peer_host=false

ssl_version=MAX

type=server

[dbreplica]

address=teste-maxscale-read.[...].com

extra_port=0

persistmaxtime=0ms

persistpoolmax=0

port=3306

priority=0

protocol=mariadbbackend

proxy_protocol=false

rank=primary

ssl=false

ssl_cert_verify_depth=9

ssl_verify_peer_certificate=false

ssl_verify_peer_host=false

ssl_version=MAX

type=server

[rwsplit-listener]

type=listener

address=::

authenticator_options=

port=3306

protocol=mariadbclient

service=rwsplit-service

ssl=false

ssl_cert_verify_depth=9

ssl_verify_peer_certificate=false

ssl_verify_peer_host=false

ssl_version=MAX

type=listener

[rwsplit-service]

type=service

router=readwritesplit

user=maxusr

password=FFC7...

enable_root_user=false

max_connections=0

connection_timeout=0

net_write_timeout=0

auth_all_servers=false

strip_db_esc=true

log_auth_warnings=true

session_track_trx_state=false

retain_last_statements=-1

session_trace=false

rank=primary

connection_keepalive=300s

causal_reads=false

causal_reads_timeout=10000ms

delayed_retry=false

delayed_retry_timeout=10000ms

disable_sescmd_history=false

lazy_connect=false

master_accept_reads=false

master_failure_mode=fail_on_write

master_reconnection=true

max_sescmd_history=1500

max_slave_connections=255

optimistic_trx=false

prune_sescmd_history=true

retry_failed_reads=true

slave_connections=255

slave_selection_criteria=LEAST_CURRENT_OPERATIONS

strict_multi_stmt=false

strict_sp_calls=false

transaction_replay=false

transaction_replay_attempts=5

transaction_replay_max_size=1073741824

transaction_replay_retry_on_deadlock=false

use_sql_variables_in=master

targets=dbmaster,dbreplica

Anything you see which blocks connections to be also opened to the dbreplica? The above is a `cat --persistir/*` so I can collect all configurations. Do you think this can be a side effect of using dynamic commands to set up a replication cluster on MaxScale?

Thanks! 

[Markus Mäkelä]

Hi,

I think it might be related to the replication topology resolution in the monitor and how the replication is configured to use the RDS hostnames. I think you could try using assume_unique_hostnames=false and check if that helps: usually you see the Slave of External Server, Running only when the monitor thinks a server is replicating from outside of the set of configured servers.

Markus

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[Wagner Bianchi]

Thanks, Markus! Setting up the assume_unique_hostnames=false made it.

dbmaster      teste-maxscale.[...].com         3306    2       Master, Running
dbreplica     teste-maxscale-read.[...].com    3306    2       Slave, Running

Thanks!

-- Wagner Bianchi Oracle ACE Director Splunk Certified Architect AWS Certified Solutions Architect Oracle Certified Expert (OCE/MySQL) Official Certified MariaDB Professional, 10.3 MariaDB RDBA Team Lead @ MariaDB RDBA Team +55.31.8654.9510 m...@wagnerbianchi.com www.wagnerbianchi.com wbianchijr